Cytodiagnosis is known as a method for diagnosing diseases by detecting abnormal cells contained in specimens such as sputum, urine, pleural effusion, ascites, bile, aspirates, or sample extracted from uterine cervix. Abnormal cells contained in these specimens are detected on the basis of cell morphology, stained conditions, and other information through the use of, for example, microscopy or flowcytometer after nucleic acid staining or immunostaining.
In cytodiagnosis, cells in a specimen are kept as they are, subjected to staining and other treatments before tests, and then subjected to microscopy or various analyses. Accordingly, it is important to store the cells as they are without being influenced by proteolytic enzymes and others contained in the specimen. Such storage is carried out usually by fixing the cells.
As a method for cell fixation, liquid phase fixation is known, wherein cells are stored in a liquid containing formaldehyde, alcohol, or the like.
For example, as a method of immunostaining fixed cells with a labeled antibody, it is known to activate the antigen of the fixed cells to expose the antigen thereby allowing combination of the antigen with an antibody.
For example, U.S. Pat. No. 6,960,450 discloses a method for activating the antigen of formalin-fixed cells on a glass slide with methylmaleic anhydride.
However, under the conventional method for activation of antigen, a fixed cell must be heated to a temperature of 60 to 121° C. to activate the antigen. In particular, the cells may be damaged by heat applied during the activation of the antigen of the liquid-phase fixed cells, which may hinder precise diagnosis.